Session: 02-03 Thermal and Environmental Barrier Coatings

Paper Number: 81964

81964 - Assessing the Structural Integrity of Plasma-Sprayed Multilayer Thermal Barrier Coatings 

The application of heat resistant coatings with low thermal conductivities is one of the most beneficial technologies in order to reduce the detrimental effects of the high temperature environment on the structural components, e.g. heat shields, turbine vanes and blades, of modern gas turbines. Nowadays, thermal barrier coatings (TBCs) are typically made out of yttria-stabilized zirconia (YSZ). Unfortunately, the long term operation temperature of YSZ is limited to 1200 °C. In order to achieve higher process temperatures and thereby increase the efficiency of gas turbines, new ceramics and coating architectures have to be implemented. One of the most promising attempts is the integration of gadolinium zirconate (GZO) and it’s combination with YSZ to build a multilayer ceramic coating. GZO has the capability to withstand temperatures up to 1500 °C without significant degradation. Furthermore, it leads to a greatly improved thermal insulation compared to YSZ. Since the components lifetime is strongly influenced by the reliability of the coating system, assessing the structural integrity of the material compound at any time during an envisaged operation becomes an important aspect in life prediction. The majority of lifetime models associates the failure of TBCs to an oxidation of the bond coat (BC). A thickening of the thermally grown oxide leads to a conversion of stresses at the undulated YSZ-BC interface, supporting the propagation of existing micro cracks. However, in multilayer TBCs a shift of the failure site from the YSZ-BC interface to the GZO-YSZ interface has been observed. Thus, an exclusively oxide-based formulation is not sufficient to describe the damage transition phenomena. Therefore, this paper outlines a mechanism-based approach for assessing the structural integrity, considering all relevant thermally activated processes as well as the interaction between thermal and elastic misfits. Oxidation of BC, creep of compound materials and sintering of ceramics are modeled in terms of temperature and exposure time. Finite element analysis of GZO-YSZ pairings with different microstructures reveal a strong influence of the initial porosities on the sintering behavior and thus on the resulting mechanical stresses and potential crack driving forces at the bi-material interfaces.

Presenting Author: Marcel Adam Technical University of Darmstadt

Presenting Author Biography: Since 2016: Research Associate, Chair and Institute for Materials Research, Technical University of Darmstadt<br/>2012 - 2015: Master&#39;s degree, Mechanical and Process Engineering, Technical University of Darmstadt<br/>2009 - 2012: Bachelor&#39;s degree, Mechanical and Process Engineering, Technical University of Darmstadt<br/>2003 - 2008: Jet Engine Mechanic, MTU Maintenance Hannover

Authors:

Marcel Adam Technical University of Darmstadt
Matthias Oechsner Technical University of Darmstadt
Christian Kontermann Technical University of Darmstadt